Erections: What we learned from mice could help sexual health in men

Have you ever wondered how a penile erection works, but never dared to ask? Imagine a dry sponge in a condom. Now pour water on the sponge (that’s the blood flowing in). There you have it.

This “penis sponge” is scientifically called corpora cavernosa. Erections depend on the inflow and retention of blood. Smooth muscle cells regulate blood flow to the sponge and its subsequent firmness. In a recent study, my colleague and I delved into the role of penile fibroblasts, the most abundant cells in the human penis, about which little was previously known.

We found that penile fibroblasts help smooth muscle cells relax. Using a technique to make cells light-sensitive, we were able to activate fibroblasts by shining blue light from outside on the penises of mice.

We found that light-induced activation of fibroblasts relaxed smooth muscle cells and increased blood flow. The effectiveness of this relaxation support depends on the number of fibroblasts. More fibroblasts led to easier relaxation and increased blood flow.

We also learned that the number of fibroblasts is not static and identified the signaling molecules that regulate the number of fibroblasts in the penis. By removing or overexpressing the relevant molecules, we could increase or decrease the number of fibroblasts and see corresponding changes in penile blood flow in response.

But we quickly learned that too many fibroblasts have negative consequences. Mice with very high numbers of penile fibroblasts showed erections that lasted for several hours. In men, this corresponds to a painful pathological condition called priapism, which requires a visit to the hospital.

Can penile erection be trained? In humans, much of the “erection training” occurs naturally during sleep, with men experiencing three to five erections per night, known as “nocturnal penile tumescence.”

To test the importance of training, we artificially changed the frequency of erections in mice by targeting the brain region responsible for initiating an erection. This technique allowed us to turn erections on and off by simply administering a designer drug that specifically activated the responsible nerve cells in the brains of mice.

More fibroblasts, more blood flow

Surprisingly, we found that the number of penile fibroblasts changed in relation to the frequency of erections. The more frequent the erections, the more fibroblasts were present and the better the blood flow. This means that it becomes easier to initiate and maintain an erection with an increased erection frequency.

It is known that unconscious ‘training’ during sleep decreases with age. Aging is one of the main risk factors for erectile dysfunction in men.

When studying penises from old mice, we found that they had lower numbers of fibroblasts compared to young mice. When reducing the number of recurring erections in young animals for a long period of time, we found a decrease in the number of fibroblasts and lower blood flow to the penis.

One interpretation could be that reduced training has a negative effect on the number of fibroblasts and therefore makes it less efficient to initiate an erection.

Although the spontaneous occurrence of erections during sleep is certainly useful, our study suggests no differences between involuntary and actively induced erections in the number of penile fibroblasts. Thus, an age-related decrease in nocturnal penile tumescence could be a potential target for future treatment of erectile dysfunction or could be compensated by actively achieving an erection.

Our research reveals a mechanism for controlling penile erections, opening the door for further research to understand and improve sexual health.The conversation

Christian Göritz, Associate Professor, Department of Cell and Molecular Biology, Karolinska Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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